Science Musings Blog

Monday, December 22, 2008

Le rayon bleu?

I am writing this yesterday, Sunday. I have just come back from watching sunrise on the beach. The Sun rose at 6:41 AM. The winter solstice was at 7:04 AM. So I was watching the Sun rise at almost exactly its southernmost point along the horizon. Tomorrow it will begin its long crawl back to the north.

From where I stood in front of the house, the Sun rose just at the beacon monument on the highest point of Stocking Island, the outer barrier of Georgetown Harbor, about nine miles away. It was almost as if that pillar of stone had been erected for me, as a marker for the solstice. There is no marker at the northern end of the Sun's horizon crawl, only flat sea.

Our island lies athwart the Tropic of Cancer. At the summer solstice the Sun tracks exactly overhead, beating down like a hammer. We'll be long gone by then.

I watch, every morning, because it is the most magical time of the day, because its fun to watch the Sun creep along the barrier islands near Georgetown, and because I am always anticipating the green flash, le rayon vert, that sudden blink of emerald light at the moment the Sun breaks the horizon (or sinks below it), a trick of scattering, absorption, and refraction. As readers of Honey from Stone and Natural Prayers will know, I searched for it for years, from three continents, morning and evening, on desert horizons and sea horizons, unsuccessfully. And now, with so many sunrises over so flat a horizon, the gift of green has become almost commonplace.

In his masterful book The Nature of Light and Color in the Open Air, M. Minnaert mentions the even rarer possibility of a blue, or even violet flash. I suppose I have that to look for, although after so many hundreds of sunrises I'm beginning to wonder if even Minnaert had seen it. Has anyone reading here ever seen a flash of blue?